EXPRESSION OF KAINATE-SELECTIVE GLUTAMATE-RECEPTOR SUBUNITS IN GLIAL-CELLS OF THE ADULT BOVINE WHITE-MATTER

It is now well established that glial cells, like neurons, express a l arge variety of non-NMDA glutamate receptors. However, knowledge about the subunits forming the receptors and the types of glial cells which express them is incomplete. The aim of this study was to determine th e presence and distribution of kainate-preferring glutamate receptor s ubunits in glial cells in the white matter of adult cattle. To this en d, reverse transcription and polymerase chain reaction (RT-PCR) analys is of mRNA extracted from the corpus callosum, fornix and optic nerve of brains of adult cattle was carried out using specific primers that allowed selective amplification of the kainate transcripts encoding th e GluR5, GluR6, GluR7, KA1 and KA2 subunits. In the three areas studie d, transcripts for all five subunits were detected. Restriction digest ion of the amplified products confirmed the specificity of the PCR amp lifications and showed that the extent of Q/R editing in the GluR6 sub unit was lower than that described in the rat whole brain. Immunohisto chemical experiments revealed that GluR5-7 and KA2 subunits appeared i n similar to 50% of astrocytes and 40% of oligodendrocytes. In astrocy tes the receptor subunits were located throughout the cell body and pr ocesses, whereas in oligodendrocytes they were mostly restricted to th e soma. Double-labelling studies demonstrated that in the white matter areas studied GluR5-7 and KA2 subunits are coexpressed in the majorit y of macroglial cells endowed with kainate receptors. In addition, ast rocytes, but not oligodendrocytes, expressing kainate-selective recept ors were found to possess the GluR1 subunit, an alpha-amino-3-hydroxy- 5-methyl-4-isoxazole propionic acid (AMPA) receptor subunit which has previously been found in this macroglial cell type. Taken together, th ese results provide evidence for the presence and molecular diversity of kainate-selective receptor subunits in glial cells of the adult whi te matter and for their coexpression with AMPA receptor subunits. The widespread distribution of kainate receptors in glial cells of the whi te matter suggests that these receptors may be important in axon-to-gl ia and/or glia-to-glia signalling.